Pests, particularly pest pests, remain a worldwide economic and public health concern. Agricultural damage due to pests amounts to billions of dollars annually; pests are vectors for some of the world's most deadly diseases; invasive species are of increasing concern worldwide. For these reasons, among others, control of pest populations remains a major societal concern.
One approach to control of pest populations has been the use of pesticides. Pesticides suffer from many problems, however. Synthetic pesticides, for example, tend to be poisonous, carcinogenic, or teratogenic. Since many of these pesticides are not (or are only slowly) biodegradable, the concentration of these substances in body tissues tends to increase up the food chain, a tendency that has led to disastrous effects on the populations of primary predators in many ecosystems.
There has thus been much recent effort devoted to development of “natural” means and methods of pest control, particularly those based on plant-derived chemicals such as pyrethroids. Even “natural” pesticides, including pyrethroids, suffer from the problem of pest resistance, however. As mutations that enable the pests to metabolize the active ingredient of the pesticide spread through the pest population, the effectiveness of the pesticide decreases in consequence.
In many applications, pesticidal activity is not necessarily required, and pest repellent activity is sufficient. Since the activity of pest repellents does not necessarily involve interruption of a metabolic process, repellents are inherently less likely to lead to problems of resistance. A number of disclosures of pest repellent activity of plant extracts have been made, and the ability of extracts of plants such as garlic and neem tree are well-known. Representative disclosures of plant extract-based pest repellents include U.S. Pat. No. 5,736,584 (cactus extract) and U.S. Pat. No. 7,179,479 (Foeniculum vulgare [fennel]); U.S. Pat. Appl. Pub. Nos. 20030124165 (Tarchonanthus camphoratus [camphor bush]); 20050019432 (evening primrose); 20061530890 (Spiraea), and 20120015054 (Euodia); and PCT Pat. Appl. Nos. WO0004780 (Callitris columellaris [cypress pine]), WO07148105 (Mentha, Eucalyptus, Citrus, Lavendula, Rosemarinus, Thymus, Juniperus, Eugenia), WO12018152 (oak vinegar extract), and WO12018153 (Phellodendron [cork tree]).
Extracts of Achillea spp. (yarrow) have been used in pesticidal compositions; see, for example, Hungarian Pat. No. 50592, U.S. Pat. No. 8,062,676, and U.S. Pat. Appl. Pub. Nos. 20070098570 and 20100144888.
Despite the research effort put into development of pesticidal and pest repellent plant extract based compositions, development of economically viable plant extract based pest repellents, particularly those that are useful in agricultural applications, remains a long-felt yet unmet need.